1. Field of the Invention
The present invention relates to a color measuring device, an image forming apparatus, a colorimetric system, and a color measuring method.
2. Description of the Related Art
In an image forming apparatus such as printers, processing called color management is performed in order to suppress fluctuation of an output by a characteristic specific to a device and increase reproducibility of an output to an input. For example, the color management is performed by the following technique. First of all, an image of a color chart (patch) of a reference color is actually output by an image forming apparatus, and a color measuring device measures the color of the patch. Hereinafter, the patch whose color is measured is referred to as a “colorimetric target patch”. Then, a color conversion parameter is generated based on a difference between a colorimetric value of the color-measured colorimetric target patch and a colorimetric value of a corresponding reference color in a standard color space, and the color conversion parameter is set to the image forming apparatus. Thereafter, when outputting an image corresponding to input image data, the image forming apparatus performs color conversion on the input image data based on the set color conversion parameter, and outputs an image based on the image data which has been subjected to the color conversion. Consequently, the image forming apparatus can output an image with high reproducibility in which fluctuation of an output by a characteristic specific to a device is suppressed.
In this color management, a spectrophotometer is widely being used as color measuring device that performs colorimetry on the colorimetric target patch. The spectrophotometer can obtain spectral reflectivity for each wavelength and thus perform high-accuracy colorimetry. However, since the spectrophotometer is expensive, it is desirable to perform high-accuracy colorimetry using a cheaper device.
An example of a technique of implementing colorimetry at a low is a technique of capturing an image of a colorimetric target as a subject by an image capturing device with an image sensor and converting a RGB value of the subject obtained by the image capturing into a colorimetric value in the standard color space. For example, Japanese Patent No. 3129502 discloses a technique in which a reference color chart serving as a comparative target of a subject is placed near the subject serving as a colorimetric target, the subject and the reference color chart are simultaneously captured by a color video camera, RGB data of the subject is corrected using RGB data of the reference color chart obtained by the image capturing, and then the RGB data of the subject is converted into a colorimetric value in the standard color space.
However, in the technique discussed in Japanese Patent No. 3129502, it is difficult to maintain a positional relation among the subject, a light source, and the color video camera, and an imaging condition changes each time image capturing is performed. Thus, it is likely that it is difficult to obtain stable image data from the subject of the colorimetric target.
Therefore, there is a need to provide a color measuring device, an image forming apparatus, a colorimetric system, and a color measuring method, which are capable of acquiring stable image data from a subject of a colorimetric target and thus performing high-accuracy colorimetry.